Many electrographic printers/copiers use rollers to feed material to a nip near a web. A pressure sensitive roller and a heated roller form a nip. During fusing, after printing, the pressure sensitive roller and heated roller are in pressure contact with one another in what is referred to as contact fusing. If heated rollers do not contact the substrate it is referred to as non-contact fusing.
In electrographic printers many of the non-contact fusing systems have suffered from the absence of a contact roller for toner dot spreading, which acts as an assist for toner/substrate surface wetting and gloss modulation. This is due to the fact that the surface finish of the roller coating is normally used to act as a gloss modulator in contact fusing systems but is not available in the non-contact fusing systems currently available. Without the use of the roller, the non-contact fuser can cause large differences in toner gloss (luster) from light scattering off of separate toner particles at low to mid range color densities that produce low gloss, and solid high density layers of toner that produce high gloss. Rollers tend to modulate the gloss to near the finish of the roller coating except when toner particles are separated enough to scatter light at low lay-downs (or low to mid range color densities), where the rollers tend to spread the toner dots to reduce the light scattering effect that produces low gloss.
Non-contact systems toner formulations can also produce various limitations for non-contact fusing image quality. Many non-contact fusers operate in conjunction with a toner that has a sharp melting point and attains a low enough viscosity to attain a high gloss level at high toner lay-downs (highest color densities). These toner types tend to have other associated problems such as cratering which leads to poor quality results. Cratering can be attributed to volatiles escaping through a molten toner layer: gasses push their way through the molten toner layer leaving a toner void surrounded by a rim of toner that looks very similar to a volcanic crater, or a meteor crater. In some cases the non-wetting of the toner melt can lead to image artifacts such as lower gloss and image density in a manner similar to cratering. The chilled finish roller described below works in conjunction with toners with crystalline additives to overcome these difficulties and produce a high quality product.